The invention relates to a sensor array communications system in which time division multiplexing is used to enable any one of multiple sensors in a selectively accessed access order.
Sensors for detecting physical characteristics of ocean environments tend to be expensive and complicated, and are typically incorporated into array systems which are heavy, bulky, and power hungry. Deployment and recovery of sensor array systems intended to be moored to the bottom of the ocean generally requires large expenditures of manpower and ship time. A continuing need exists for sensor array systems which are easy to deploy and recover, as well as inexpensive to manufacture.
One type of sensor system intended to solve this continuing need is taught in U.S. Pat. No. 5,272,476, "Data Acquisition System Having Novel, Low Power Circuit For Time-division Multiplexing Sensor Array Signals." The '476 patent describes multiple transceivers linked to a control circuit by a two-wire signal transmission line. The system employs time division multiplexing to enable each of the transceivers in a non-varying sequence and at a sequence rate which is cyclically repeated. This type of system performs well when it is desirable to obtain data from each of the transceivers at the sequence rate and cycle periodicity, as for example, in applications where all of the sensors are of the same type. For example, in an acoustic array, it may be desirable to repeatedly sample the data from acoustic sensors, one at a time, and to re-sample such sensors at periodic intervals. However, for sensor arrays which include different types of sensors, such as compass direction sensors, acoustic sensors, salinity sensors, and/or current flow sensors, it may be preferable to sample the sensors at different rates. For example, ocean conductivity typically changes at a rate many orders of magnitude less than the rate at which the acoustic properties of the environment may changes. For a sensor array comprised of conductivity and acoustic sensors, it would be wasteful of the generally limited electrical power capacity and the limited data transmission rate of the data transmission line of the system to repeatedly sample them at the same rate over and over. Another disadvantage of the '476 system is that it requires that the TDM transceivers be linked to the control circuit "C" with at least four wires, or three wires with a sea water ground.
Therefore, a continuing need also exists for a sensor array system comprised of multiple sensors in which each of the sensors may be sampled any number of times, and in either a random or non-random order, depending upon the requirements of a particular application. A further need exists for a system in which the sensors are linked to a central processor by less than three wires to reduce system costs, bulk, and hydrodynamic drag.